Battery Light Comes on When Idle – Causes & Fixes

Over time, the battery in your car will slowly lose its ability to hold a charge. When this happens, the battery light on your dash may come on when the vehicle is idling. If this happens, it’s important to take your car to a mechanic as soon as possible to have the battery checked out. But why does the battery light comes on when idle?

The battery light is a warning light that comes on when your car’s battery is not charging correctly. This may lead to your car stalling or not starting at all. If the battery light comes on while you are driving, your car is not charging the battery, and the battery will eventually run out of power. Additionally, your check gauge light might come on as well.

Why Does My Battery Light Come On When Idling? 

There are a few reasons your battery light may come on when idling. A bad battery, corroded terminals, alternator problems, or loose wiring are some of the most common causes.

I will discuss the most frequent reasons for which the battery light might come on when idling below.

battery warning light on dashboard

Bad Battery

A bad battery is the most common reason for this warning light to stay on. If you have a voltmeter, you can check the voltage of your battery. A good battery should have a voltage of around 12.45 volts. If the voltage is lower than this, it means the battery is not holding a charge and needs to be replaced.

If you don’t have a voltmeter or are not sure how to test a car battery, drive to the closest garage and have a professional check it for you.

Corroded Terminals

You can also check the battery terminals for corrosion. If they are corroded, it means the battery is not getting the proper connection and needs to be cleaned or replaced.

A visual inspection will quickly tell you whether or not the battery terminals are functioning correctly. Here is a useful guide on how to clean your terminals and battery if they are corroded.

Alternator Problems

The alternator is what charges the battery while the car is running. If the battery light is coming on, it could be a sign that the alternator is not charging the battery correctly. You can check the alternator by starting the car and then disconnecting the positive battery terminal. If the car dies, it means the alternator is not working correctly and needs to be replaced.

Loose or Damaged Wiring

When the battery light is coming on, it could also be a sign of loose or damaged wiring. The best way to check this is to take the car to a mechanic and have them check the wiring for you. Wires typically break around the connectors rather than further up the wiring harness.

You can also do this yourself, but be prepared to spend a couple of hours meticulously checking every inch of wiring.

Related content: Why would my brake and battery lights come on at the same time?

Bad Ground Strap

The ground strap is what helps to complete the electrical circuit. If this is damaged or not connected correctly, it can cause the battery light to come on. The ground strap is usually located on the engine block or chassis. You can check the ground strap by using a voltmeter to test for continuity. If there is no continuity, the ground strap needs to be replaced.

Bad Or Loose Battery Cable

The battery cables carry the electrical current from the battery to the starter. If these are damaged or loose, it can cause the battery light to come on. The best way to check the battery cables is to use a voltmeter to test for continuity.

Signs Of A Bad Battery

Batteries will lose their ability to hold a charge with time and may need to be replaced. There are several signs that your battery is going bad:

mechanic replacing bad battery

The Battery Light on Your Dash Comes on When the Car Is Idling

One of the most common signs of a bad battery is when the battery light on your dash comes on while the car is idling. The battery warning light is usually yellow or red, and it indicates that your battery is not being charged properly.

The Engine Cranks Slowly When You Try to Start the Car

Another common sign of a bad battery is when the engine cranks slowly when you try to start the car. There are several things that can cause this, but a bad battery is one of the most common causes.

The car Won’t Start at All

This is usually caused by the battery being unable to hold a charge.

You Notice That Your Car Isn’t Holding a Charge as Long as It Used To

This is another typical indicator that your battery is dying. If you notice that your car isn’t holding a charge as long as it used to, it’s probably time to replace the battery.

Frequent Jump Starts

Having to jump-start your car frequently is another sign that your battery is going bad. If you find yourself jump-starting your vehicle more than once a month, it’s time to get a new battery.

Dim Headlights

When you notice that your headlights are dimming, it could signify a bad battery. This is usually caused by the battery being unable to hold a charge.

Related content: How Can A Bad Battery Cause A Car To Misfire?

Frequently Asked Questions

So now you know the possible reasons for a battery light when the car is idling but perhaps have further questions. Below is a short section answering the most popular questions about the subject.

How Much Does It Cost To Fix A Bad Battery?

The cost of fixing a bad battery can vary depending on the severity of the issue. If it is a simple fix, such as replacing a corroded battery terminal, the cost will be relatively as low as $45 to $250. However, if the problem is more severe, such as a faulty alternator, the repair cost can be much higher, between $200 and $350.

Why Does My Voltage Drops At Idle, And Picks Up While Driving?

One reason your voltage may drop at idle is if your alternator isn’t working correctly. The alternator charges the battery while the car is running, so if it’s not working properly, the battery won’t get charged, and the voltage will drop. Another reason for this could be loose or damaged wiring. If the wiring is damaged, it can cause an interruption in the electrical current, which will cause the voltage to drop.

Is It Safe To Drive With A Bad Battery?

It is not safe to drive with a bad battery. If the problem is severe, such as a faulty alternator, the car may stall and cause an accident. If the problem is less severe, such as a corroded battery terminal, the vehicle may still have difficulty starting and may run slowly.

How Can I Prevent My Battery From Going Bad?

There are a few things you can do to prevent your battery from going bad. First, make sure to keep your car’s battery clean. Second, avoid overcharging your battery. Third, keep your car’s alternator in good working condition.


A battery light that is on should never be treated lightly. It can result in car stalling and potential loss of control while driving. If you experience this problem, I recommend having a mechanic inspect the vehicle as soon as possible.

They will be able to check the battery, wiring, and charging system in order to discover the cause of the issue. They will be able to give you an exact cost for repairing your car.

As always, sticking to a strict maintenance schedule and performing regular health checks for your vehicle will prevent you from any troubles or hefty repair bills.